add dirstate._dirtypl variable...
add dirstate._dirtypl variable
Theoretically, it's possible to forget modified dirstate
parents by doing:
dirstate.invalidate()
dirstate.setparents(p1, p2)
dirstate._map
The final access to _map should call _read(), which will
unconditionally overwrite dirstate._pl.
This doesn't actually happen right now because invalidate
accidentally ends up rebuilding dirstate._map.
